On the nights of September 10-12, 2017, you might see the moon rising in the east before your bedtime if you’re a night owl. But you’d be better off to wake up before dawn to see the moon in front of the constellation Taurus, higher up in the predawn sky. Look first for the moon, then seek out Taurus’ two prominent signposts: the star Aldebaran and the tiny, dipper-shaped Pleiades star cluster. The moon is about to take dead aim on Aldebaran and hide it from view.
Every month, as the moon makes its rounds in front of the constellations of the zodiac, it always travels in front of the Taurus for several days. On September 10, the moon is moving toward Aldebaran on the sky’s dome. Depending on where you live worldwide, the moon will pass to the north of this star, south of this star, or will occult (cover over) this star.
If you live in Hawaii or the West Coast of North America, you’re in a position to watch this lunar occultation of Aldebaran before dawn on September 12. As always, the illuminated side of the waning moon points in the moon’s direction of travel: eastward. So Aldebaran will disappear behind the moon’s illuminated side and then reappear on the moon’s dark side.
The worldwide chart above shows where this occultation of Aldebaran happens on September 12. The area in between the white lines shows where the occultation occurs in a nighttime sky. The short blue lines depict where the occultation take splace at morning dawn and the red lines where the occultation is in a daytime sky. For your convenience, we give the occultation times for four different localities in local time (no coversion necessary):
Lunar occultation of Aldebaran on September 12, 2017
Occultation begins: 4:03:05 a.m. local time
Occultation ends: 4:23:35 a.m. local time
Occultation begins: 4:46:12 a.m. local time
Occultation ends: 5:52:26 a.m. local time
San Diego, California
Occultation begins: 4:37:08 a.m. local time
Occultation ends: 5:49:41 a.m. local time
Occultation begins: 12:31:04 a.m. local time
Occultation ends: 1:34:52 a.m. local time
Eastern Daylight Time: UTC – 4 hours
Central Daylight Time: UTC – 5 hours
Mountain Daylight Time: UTC – 6 hours
Pacific Daylight Time: UTC – 7 hours
Alaska Daylight Time: UTC – 8 hours
Hawaiian Standard Time: UTC -10 hours
Bottom line: Even if you miss the lunar occulatation of Aldebaran, you can still watch the waning moon traveling eastward in front of the constellation Taurus the Bull over the next several mornings.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.